Researchers from QuTech report in Nature today a novel method for ‘reading’ qubits that may help effort to build larger, better controlled quantum computer systems. Their approach, described in a brief article on the QuTech website, is based on so-called spin qubits in quantum dot arrays.
Quantum dots are very tiny islands that can each confine one or multiple electrons and are tunnel coupled to their neighbors. The spin of the electron acts as a qubit. Spin qubits in quantum dots are read out via a very sensitive detector that measures the charge in its environment.
“Charge sensors work well, but only locally: they need to be in close proximity to the charge they measure. Scaling up the current approach towards a large number of interconnected qubits will therefore limit qubit connectivity, because we would need to place sensors close to all qubits,” said Sjaak van Diepen, of QuTech lead author of the Nature article (Electron cascade for distant spin readout).
“Our new readout method is based on a phenomenon that all of us know from our childhood: toppling dominoes,” said Diepen in the QuTech article. “A first transition triggers a second transition, a second transition triggers a third transition, and so on – much like dominoes toppling over in a chain reaction.”
Here’s an excerpt from the paper’s abstract:
“[W]e show that the Coulomb repulsion allows an initial charge transition to induce subsequent charge transitions, inducing a cascade of electron hops, like toppling dominoes. A cascade can transmit information along a quantum dot array over a distance that extends by far the effect of the direct Coulomb repulsion. We demonstrate that a cascade of electrons can be combined with Pauli spin blockade to read out distant spins and show results with potential for high fidelity using a remote charge sensor in a quadruple quantum dot device.”
Intel is betting big on spin qubits based on quantum dots which can be manufactured using its CMOS process. The company says its manufacturing expertise combined with silicon dot qubit strengths, notably long coherence times, are well-suited for eventually building large-scale quantum computers. (See HPCwire article, Intel Connects the (Quantum) Dots in Accelerating Quantum Computing Effort)
QuTech was founded in 2014 as a collaboration between Delft University of Technology (TU Delft) and the Netherlands Organization for Applied Scientific Research (TNO). It is positioned as separate research institute within the TU Delft organization.
Link to Nature paper: https://www.nature.com/articles/s41467-020-20388-6